1. Field of the Invention
The present invention relates to methods and apparatus for ink jet printing capable of high quality image formation on printing materials. In particular, the present invention relates to a method and apparatus for ink jet printing which discharges a liquid which can insolubilize or precipitate coloring materials in inks.
The present invention is applicable to all instruments and devices, e.g. printers, copying machines and facsimiles, using various recording materials, such as paper, cloth, nonwoven fabric and transparency sheets for over head projectors (OHP sheets).
2. Description of the Related Art
Ink jet recording apparatus are capable of high density and high speed recording operations on various printing materials, such as paper, cloth, plastic films and OHP sheets, and have been practically used in output means of information processing systems, e.g. printers of copying machines, facsimiles, electron typewriters, word processor and work stations and handy or portable printers provided with personal computers, host computers, optical disk devices and video devices.
Each ink jet recording apparatus has its own configuration depending on the characteristic function of the apparatus and the operation circumference. A typical ink jet recording apparatus is provided with a carriage bearing a recording means, i.e., a print head, and an ink vessel; a transfer means for transferring recording materials; and a controlling means for controlling them. The print head which discharges ink droplets from a plurality of discharging nozzles is serially scanned along the main scanning direction perpendicular to the sub-scanning direction, in which a recording material travels, while intermittently carrying the recording material in response to non-recording regions. This process includes recording with ink droplets discharged on the recording material in response to recording signals and has practical advantages, for example, low running costs and low printing noise. A multiple print head having many ink discharging nozzles along the sub-scanning direction in a straight line can record a width corresponding to the nozzle array every scan on the recording material, and enables high speed recording operation.
Recently, an apparatus, which uses three or four color print heads and is capable of full color image formation, has been practically used. Such an apparatus is provided with three or four print heads and ink vessels corresponding to three primary colors of yellow (Y), magenta (M) and cyan (C), or four inks of these three primary colors and black (B).
Conventional ink jet printing methods and apparatus have unresolved issues, i.e., prevention of color mixing between black (B), yellow (Y), magenta (M) and cyan (C), high density black image formation, and prevention of feathering or bleeding. Improvement in one of these areas typically makes other problems worse. Therefore, these methods and apparatuses barely achieve high quality color printing which can respond to user's needs, as set forth below in detail.
Printing of a color image on plain paper by an ink jet printing process generally uses three or four fast set inks which can rapidly penetrate into plain paper. The fast set inks do not bleed at boundary regions of different colors in a color image, but they exhibit a low color density at each black image section and a low coloring characteristic at each colored image section other than black. Further, printing of line images such as characters causes ink bleeding along paper fibers or so-called feathering. In particular, characters of a black ink have noticeable feathering compared to those of other color inks, and are blurred and unclear. As a result, the overall quality of the recorded image is unsatisfactorily decreased.
A high quality image having a high black image density without feathering on plain paper generally requires a considerable amount of discharge of an ink having a relatively low penetration speed. However, this method forms color mixing between the black ink and other color inks at each boundary between black image sections and other color image sections, resulting in noticeable deterioration of the recorded image quality.
Practical examples for solving such drawbacks include promotion of ink drying by a heater provided in the recording apparatus. Although this method can form a color image having high coloring characteristics without bleeding or feathering, a large size apparatus accompanied by an increased cost is necessary.
Prevention of color mixing between black and color inks, high density black image formation, and prevention of feathering or bleeding are goals that are difficult to achieve simultaneously, as described above.
Japanese Unexamined Patent Publication No: 3-146,355 discloses a method in which regions along boundaries between black and other color sections are not recorded. This method, however, deforms the recorded data.
Japanese Unexamined Patent Publication No. 4-158,049 discloses a method in which images are recorded with a plurality of color heads and a character print head by switching these heads in response to the image to be recorded. However, a black image recorded with any color head is different from a black image recorded with the character print head, due to quality differences between the heads.
Another method for preventing bleeding at boundaries between black and color sections includes formation of black regions along the boundaries by means of superposition printing with color inks. A black color is also obtainable by superposing or mixing three colors (Y, M and C), but it appears faded.
Japanese Unexamined Patent Publication Nos. 56-84,992 and 64-63,185 disclose methods which use liquids for insolubilizing dyes in inks. In Japanese Unexamined Patent Publication No. 56-84,992, a material for fixing dyes is previously applied to a recording material. However, this method requires a particular recording paper, a large apparatus accompanied by an increased cost, and still leaves an unsolved problem in that it is difficult to stably apply the material for fixing dyes to the recording material of a given thickness.
Japanese Unexamined Patent Publication No. 64-63,185 discloses a technology for adhering a colorless ink to insolubilize dyes to the recording material with an ink jet print head. According to this technology, the dot size of the colorless ink is larger than that of inks for image formation, and thus the resulting image quality is satisfactory even if the printed positions of the colorless ink and the inks for image formation shift with respect to each other. However, a relatively large amount of colorless ink is discharged to a position at which an image is formed. Therefore, a longer time period for drying is required, and the resulting image is occasionally unclear.
Japanese Unexamined Patent Publication No. 7-195,823 achieves single-pass color printing in which a colorless precursor is applied to a surface of a recording material before ink jet recording.
In each image forming process using a colorless liquid to insolubilize dyes in inks and inks containing dyes, no method for controlling penetration speeds of these inks into the recording material to achieve a high quality image is disclosed or suggested.